I recently got a root request that came up as "Greenify [UID]". This looked suspicious to me as I usually get greenify requests as just "Greenify". I have tried to contact the developer of Greenify and I have yet to get a reply. Could someone clarify what "[UID]" means?
UID is the "User ID" assigned to an app.
On Android, each app runs on a separate user (for sandboxing). So on install, the system "creates" a UID/GID (UserID/GroupID) pair for new apps, which is what they are identified by. This is also used for file permissions, to ensure private data of an app stay private (and no other app can simply access them; see our file-permissions tag-wiki for details).
At install time, Android gives each package a distinct Linux user ID. The identity remains constant for the duration of the package's life on that device. On a different device, the same package may have a different UID; what matters is that each package has a distinct UID on a given device.
(Source: Android package security)
For further details, please take a look at: